Rheumatoid arthritis (referred to as RA in the following description) is one of chronic diseases with many patients, systemically causing inflammation in connective tissues. This disease induces nonspecific inflammation mainly in synovial membranes of joints, resulting in systemic multiple arthritis and injuries of cartilage and bone.
Although details of the mechanism have not been well clarified, RA has been considered to be an autoimmune disease related to lymphocyte antigen (HLA) DR4 and activated T cells (Lancet, 341, 283,1993). Since experimental animals given type-II collagen, a main structural protein of cartilage, exhibit symptoms morphologically similar to those of RA, type-II collagen is believed to be an autoantigen of this disease (J. Exp. Med., 146, 857, 1977; Lab. Invest., 54, 26, 1986).
Anti-rheumatoid (e.g., gold-derived drugs and D-penicillamine), non-steroidal and immunosuppressive drugs are widely used to treat RA. When notable effects are not obtained after administration of these drugs, steroidal ones are administered because of their effective anti-inflammatory and immunosuppressive properties.
RA treatment with the above-mentioned drugs is not radical but nosotropic. Since the steroidal drugs may cause severe side effects, it is indispensable to pay close attention to them and to always consider reduction and suspension of medication. The most preferable RA therapy is to reduce inflammation in cartilage by the disease-specific mechanism. The drugs to be used are preferably innoxious.
From these viewpoints, RA therapy based on immune tolerance has been paid attention. Immune tolerance is a phenomenon, by which such immune response as antibody production is never brought forth, even if animals are immunized with an antigen and again with the same antigen. Substances inducing such tolerance are termed tolerogens. Regarding the RA therapy by immune tolerance, it has been reported that RA is prevented by intravenous or intraperitoneal injection with such tolerogens as type-II collagen and peptides containing its partial sequence(J. Exp. Med., 170, 1999, 1989; J. Immunol., 151, 500,1993).
Although tolerogens are intravenously or intraperitoneally injected in the above-described therapy, injection through these routes is laborious. Moreover, repeated intravenous or intraperitoneal injections with these peptides to RA patients may cause severe allergy or shock. Therefore, simpler and safer RA therapy has been desired.
Functional foods capable of treating and preventing RA have also been desired, because treatment and prevention of RA by ingesting ordinary foods other than those drugs are preferable.
From these viewpoints, RA therapy by safer and simpler administration has been desired. For this purpose, treatment and prevention of RA by immune tolerance have been examined. Oral immune tolerance or mucosal immune tolerance in wide sense of the term is a phenomenon which seldom causes immune responses against an antigen, if it is taken orally. Since any antigen taken orally is absorbed through the intestinal mucosa and then processed by functions of such various tissues as Peyer's patch and epithelial cells of the intestines and the adjacent lymphocytes, portal canal and liver, administration of such antigen rarely causes allergic reaction or shock. The oral immune tolerance has been examined as immunosuppressive therapy for allergy and rejection in organ transplantation.
Intranasal administration of the antigen also induces immune tolerance which causes no systemic immune response to the antigen, since it is absorbed through the mucosa of the digestive and airway tracts and the lungs.
As for RA prevention by oral immune tolerance, prevention of collagen-induced arthritis (CIA) in mice by oral administration (intragastric administration) of native type-II collagen from bovine cartilage was reported (Proc. Natl. Acad. Sci. USA., 83, 7443,1986). This report, however, did not describe prevention of CIA with thermally-denatured type-II collagen. Another paper reported that immunogenicity (antigenicity or allergenic property) was lowered by heat treatment and that tolerogenicity of heated collagen was similar to or lower than that of native collagen (J. Clin. Invest., 69, 673-683, 1982; J. Immunol., 140,1477-1484,1988).
A recently published U.S. Pat. No. 5,399,435 described RA therapy by oral administration of the whole type-II collagen.
The present inventors studied the oral immune tolerance with type-II collagen and conditions for heat denaturation of type-II collagen, and found that thermally denatured type-II collagen was an effective tolerogen and inhibited RA contrary to the previous reports. Namely, the inventors succeeded in finding that the conditions for heat treatment of type-II collagen previously reported were insufficient for denaturation of collagen, and that collagen receiving severer thermal treatments induced more effective oral immune tolerance than did native collagen.
Moreover, the inventors succeeded in finding that denatured type-I I collagen (fragmented one) prepared with such agents as specifically recognizing the amino acid sequences of collagen also induced more effective oral immune tolerance than did native collagen.
The present invention was accomplished on the basis of such findings. The purposes of the invention were to provide oral drugs and functional foods to effectively prevent and treat RA.